In the art, devices such as heat engines and heat pumps are well known, the heat engine being a device which utilizes heat from a high temperature source to produce net power while rejecting waste heat to a low temperature sink, whereas a heat pump is a heat engine operating in a reversed cycle such that mechanical power is utilized to raise heat from a low temperature source to a high temperature sink. Conventionally, if the purpose of the heat pump is to supply heat, then it is called a heat pump. If, on the other hand, the purpose is to provide cooling, then it is called a refrigerator. If a heat engine is mechanically coupled to a heat pump (or refrigerator), such that the heat engine provides the mechanical power to operate the heat pump, then the combination is known as a heat-actuated heat pump.
In the operation of such devices, it is also well known to employ "liquid piston" means used in a hydraulic sense to transmit power from an expanding gas or to a compressing gas. Likewise, the concept of directly coupling a Stirling heat engine to a Stirling type heat pump is not new and it has also been proposed to provide free piston Stirling engines with fluid dynamic phasing between a power piston and a displacer.
In this connection, there are noted below a number of related patents and a brief description of the structure and operation in each instance.